As your husband ages, his body will steadily produce less and less testosterone. He may struggle with arousal, maintaining an erection, or ejaculation. In addition to these differences in sexual functioning, men also experience a decrease in muscle tissue, more difficulty concentrating, and less energy resulting from this hormonal change. Naturally, as a man ages, he's also at greater risk for the illnesses I'll address in the next section that further complicate sexuality.

Although a diminishing sex life may be disappointing for you as a wife, it's potentially devastating for your husband. His sexuality represents his youth, vitality, and masculinity. Be very sensitive to how you respond as you notice these changes taking place in your husband. This is a tremendous loss for him, likely coinciding with other losses, such as retirement or illness. More than ever, he will need your reassurance and love.

On the bright side, the decrease of testosterone that results from aging may have some positive effects on your marriage relationship. Your husband may become more sensitive, nurturing, and relational as his sex drive diminishes. Elevated levels of testosterone in men are linked with aggressive and competitive behaviors, while lower levels correlate with nurturing and attachment behaviors.Study conducted by Dr. Steve Gangestad and colleagues at the University of New Mexico, published in the Journal of Personality and Social Psychology 91, no. 4 (October 2006); cited in S. Dingfelder “Men Who Cheat Show Elevated Testosterone Levels,” Monitor on Psychology 37, no. 11 (December 2006), http://www.apa.org/monitor/dec06/testosterone.html. Many women report with delight that their husbands are becoming more interested in talking, bonding and relating as they age. Their husbands' decrease in testosterone and libido has opened up new avenues of relationship.

The effects of aging on sexual desire and functioning also impact a woman's sexuality. After natural or surgical menopause, a woman's level of estrogen decreases. She's likely to experience such symptoms as vaginal dryness, decreased sensitivity to touch, and decreased blood flow to the vaginal area. These typically translate into a lower sexual desire, difficulty becoming aroused, and even pain during intercourse.

Modern medicine has provided some remedies for low sex drive related to aging for both men and women. The most common are hormone therapy and medication to increase blood circulation.

Physical dysfunction

In many of the marriages represented in the 20 percent, the dynamic of their sexual relationship is simply a function of the bell curve, as described above. These couples don't fit the typical stereotypes, but their differences are completely normal. However, some couples experience an atypical sexual relationship because of some form of physical dysfunction.

A man's sex drive is determined largely by the presence of testosterone levels in his body. Although a man's level of testosterone naturally fluctuates throughout his lifetime, some men have unusually low levels, resulting in a very low sex drive.

An unusually low production of testosterone is medically referred to as hypogonadism. Testosterone in the male body is produced in the testicles. When a problem with the testicles results in low testosterone levels, it is called "primary hypogonadism." This condition can be caused by chromosomal abnormalities, complications with mumps during adolescence or adulthood, too much iron in the bloodstream, injury to the testicles, cancer treatment, and normal aging.

Hormones produced by the pituitary gland and regulated by the hypothalamus signal testosterone production in the testicles. When something goes awry in this stage of the process, the problem is referred to as "secondary hypogonadism." Hypothalamic and pituitary disorders, therefore, can cause a lack of testosterone. Inflammatory diseases, HIV, depression, thyroid disease, obesity, and certain pain and hormone medications can also contribute to secondary hypogonadism.

As if your husband's system weren't complicated enough, low sexual desire and sexual dysfunction can also result from problems with blood circulation. Just about any systemic illness can impact this aspect of sexual function, including diseases of the kidneys, lungs, liver, heart, nerves, arteries, or veins. Medications such as antihistamines, antidepressants, and high blood pressure treatments may also be culprits. Lifestyle issues such as substance abuse, smoking, and obesity, as well as the effects of stress and even prolonged bicycling, can cause erectile dysfunction.

If you feel overwhelmed by all these possibilities, remember the importance of adequate and regular medical care. Your husband may be hesitant to ask his physician about his sexual functioning. However, your encouragement, your doctor's advice, and medical intervention when necessary could make all the difference in your sex life.